In many applications, electronic equipment is interconnected and communicates with each other via a network. An example of electronic equipment interconnected in a network includes avionics, such as a radar system, on an aircraft. In order for the electronic equipment to communicate with each other, communication standards or protocol are used. One such communication standard is MIL-STD-1553.
Referring to FIG. 1, a network 10 known in the prior art uses MIL-STD-1553 communications. Remote terminals, A, B, C, X, Y, and Z are coupled to a primary bus 12 and a secondary bus 14. The primary and secondary buses 12 and 14 are controlled by a bus controller 16. Because it is often desirable to monitor data that is communicated within the network 10 in order to evaluate operation of the system, a monitor 18 is coupled to the primary and secondary buses 12 and 14 and a recorder and/or telemetry device 20 is coupled to the monitor 18.
Each of the remote terminals A, B, C, X, Y, and Z can transmit or receive at a baud rate of approximately 1 million bits per second (Mbps). Each data word is a 16-bit word, and each frame can hold up to 32 data words. Each frame starts with an address and contains a data block, and typically stands on its own. However, as noted above, the transmit and receive protocol is half duplex, such that each remote terminal transmits or receives at the baud rate.
To accommodate performance enhancements and their associated increases in data requirements, advanced systems may include a Fibre Channel network instead of a MIL-STD-1553 network. Each node on a Fibre Channel network can simultaneously transmit and receive at a baud rate of 1 gigabps (that is, a full duplex transmit-receive protocol). Each data word includes 32 bits, and each frame can include up to 528 data words. Each frame is only part of a sequence of frames, and these sequences can be part of different exchanges. Therefore, one frame is out of context without the other frames from the same sequence of an exchange.
Referring to FIG. 2A, a Fibre Channel network 22 known in the prior art is a simple connection of two Fibre Channel nodes X and Y. All of the Fibre Channel connections are single point-to-point. That is, a transmitter port T of node X is directly connected to a receiver port R of the node Y. Conversely, a transmitter port T of the node Y is directly connected to a receiver port R of the node X.
Referring now to FIG. 2B, a Fibre Channel network 24 known in the prior art includes a four port Fibre Channel switch 26. The switch 26 enables communication paths to occur simultaneously between two nodes. For example, the node A can communicate with the node C and the node B can communicate with the node D as illustrated by the dotted lines. Alternately, the node A can communicate with the node B and the node C can communicate with the node D as illustrated by the dashed lines.
With multiple switches, multiple paths can be found and, therefore, variable frame delays may result. Referring now to FIG. 3, a Fibre Channel network 28 known in the prior art includes multiple switches X, Y, and Z and nodes A and B. When using multiple switches, one path may become busy for an instant in time. This may cause a next frame in a sequence to be routed using another path, which can create different delays for each frame of a sequence. For example, the following sequence may be sent by the node A: FRAME#1, FRAME#2, FRAME#3, FRAME#4, FRAME#5, and FRAME#6. However, the sequence received by the node B may be as follows: FRAME#1, FRAME#3, FRAME#2, FRAME#5, FRAME#4, and FRAME#6. A lower level device driver of the receiving node is responsible for reordering the frames back to the original order.
As with communications in a MIL-STD-1553 networked system, it would be desirable to monitor and record data communicated within a Fibre Channel network. However, with a network switch, a Fibre Channel network can have multiple devices conversing with each other at the same time. This is because each of the ports on the switch is isolated from the other ports. Moreover, some applications may entail use of multiple switches to provide dual redundancy. Further, some applications, such as without limitation fighter aircraft, require dual redundancy. Redundancy implies that there are at least two paths between every node and that the exact same conversation will not occur simultaneously. Therefore, use of multiple switches to provide redundancy complicates even further the task of monitoring of communications within a Fibre Channel network including multiple switches.
Monitoring communications between multiple switches in a Fibre Channel network may entail intrusive modifications to hardware, such as providing special ports on switches. Also, communications that may be monitored may be limited to those that comply with certain upper level communication protocols. As a result, such monitoring may be time and labor intensive, expensive, and limited in applicability.
Thus, there is an unmet need in the art for an interface unit for monitoring communications in a Fibre Channel network that is non-intrusive, independent of upper level communication protocols, inexpensive, and easy to install.